1. Field of the Invention
The present invention relates to nitride films, and particularly methods to reduce the dislocation density in group III nitride films for semiconductor devices.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by reference numbers enclosed in brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below at the end of the Detailed Description of the Preferred Embodiment. Each of these publications is incorporated by reference herein.)
Gallium Nitride (GaN) epitaxial films are typically obtained through heteroepitaxy on sapphire, silicon carbide, or silicon substrates since single crystalline GaN substrates are still not commercially available. Due to the lattice mismatch and the different chemical nature of the individual substrates, the threading dislocation densities in GaN films are typically on the order of 108-109 cmxe2x88x922 on sapphire and silicon carbide and between 109 and 1011 cmxe2x88x922 on silicon substrates. These dislocation densities are obtained even after the application of advanced nucleation schemes, where the growth is initiated with the deposition of a very thin (Al)GaN or AlN nucleation layer at growth conditions different from the main GaN bulk layer. [1]
To further reduce the dislocation density in GaN films, several forms of epitaxial lateral overgrowth of GaN have been developed, the use of which resulted in virtually dislocation-free material in the overgrown regions. [2,3] Applying this technique, GaN-based laser diodes with a lifetime of more than 10,000 h have been obtained. [4] Furthermore, the leakage current in p-n junctions and the dark current in photodetectors could be significantly reduced. [5,6] However, epitaxial lateral over-growth involves several growth and processing steps, making it a relatively time-consuming and expensive method. Dislocation reduction has also been observed after insertion of multiple GaN or AlN nucleation layers. [7]
There is a need for methods of reducing the dislocation density in nitride films, particularly for semiconductor light emitting device applications. There is also a need for such methods which may be performed quickly and inexpensively. The present invention meets these needs.
The present invention discloses a semiconductor film having a reduced dislocation density. The film comprises at least one interlayer structure, including a group III-nitride layer, a passivation interlayer disposed on the group III-nitride layer, interrupting the group III-nitride layer, and an island growth interlayer disposed on the passivation interlayer, and interrupting the group III-nitride layer. A method of making a semiconductor film of the present invention comprises producing a semiconductor film including at least one interlayer structure, each interlayer structure produced by the substeps of growing a group III-nitride layer, depositing a passivation interlayer on the group III-nitride layer, depositing an island growth interlayer on the passivation interlayer and continuing growing the group III-nitride layer.
In one embodiment of the present invention, dislocation reduction in GaN films grown on sapphire and silicon substrates is achieved by inserting thin InGaN layers grown in a selective island growth mode after passivation of the GaN surface with a submonolayer of silicon nitride. The present invention discloses a method that is most effective at reducing the pure edge dislocation density when it is high, i.e.,  greater than 1010 cmxe2x88x922. Thus, the structural quality of typically highly dislocated GaN on silicon films is significantly improved. The results are visible in a reduction of the (0002) full width at half maximum (FWHM) from 1300 arcsec for ordinary GaN on silicon to 800 arcsec for GaN films with silicon nitride/InGaN interlayers. In the case of GaN layers grown on sapphire (dislocation densityxcx9c109 cmxe2x88x922), the method resulted mainly in a reduction of the FWHM of the (10{overscore (1)}2) and (20{overscore (2)}1) diffraction peaks.